Electric current interrupter



March 2, 1948.

s. o. FIED LE R ETAL 2,437,225 ELECTRIC C URRENT INTERRUPTER Filed Oct. 27, 1945 2 Sheets-Sheet 1 ,fn Van for:

Srumerfl 550459, mm J/mw BJOR/(STZM March s. o. FIEDLER a-r m. 2,437,225

' ELECTRIC CURRENT INTERRUPTER 'Filed 001;. 27, 1945 2 Sheets-Sheet z im/anions:

STmRr 0. 5501.59, 4N0 Jo/m/v BJORKSTEN.

. thereby making and breaking contacts.

Patented Mar. 2, 1948 smart 0. Fiedler and Johan Bjorksten, Chicago, 111.; said Fiedler assignor to Bjorksten Research Laboratories, Inc., Chicago, Ill.

Application October 27, 1945, Serial No. 625,050 6 Claims. (01. 200-32) This invention relates to a device for produc ing an interruptedv direct current, and, more specifically, to a device producing an interrupted current which is readily convertible to alternatingcurrent by means of a transformer.

Heretofore, several types of devices have been employed for this purpose, none of which has been entirely satisfactory. ,One type has been actuated by electromagnets, moving an anchor intermittently, which, in turn, intermittently makes and breaks the contact. Another type has been dependent on the instant evaporation of liquid on passage of a large amount of current, such as is obtained, for instance, when current passes through a platinum needle immersed in sulfuric acid. Other types of devices have been based on revolving mechanical elements in which firm metallic bodies have intermittently contacted and been removed from" each other, All of these prior devices have had the drawback that arcing would occur and that this arcing would cause a wear or oxidation of the contacting 'surfaces, which, in time, would interfere with the proper operation of the device.

An object of this invention is to provide a superior device for interrupting direct current, which is free from these disadvantages of prior art. Another object is acurrent interrupter in which the breaking contact is between two mercury electrodes. A further object is an interrupter where the breaking contact is between two electrodes of normally liquid sodium-potassium alloy. Another'object is a current interrupter giving an interrupted current of predeter mined wave form. Further objects will become apparent as the following detailed description proceeds, in which reference is made to the drawings, of which Figure 1 and Figure 3 are vertical sectional views, Figure 2 and Figure 4 partial sectional views, and Figures 5 and 6 are horizontal sectional views perpendicularly to Figures 1 and 3 and taken with a section through the center of the apparatus.

Referring to Figures 1 and 2, the particular embodiment of the invention shown in the drawings comprises a housing I made of ceramics, glass, plastic, or of any other insulatingmaterial of suitable mechanical properties and strength. Inside this case is a rotor 2, also made of an insulating material, and revolving around an axle 6. In this rotor are a number of insulating vanes 3 which are pressed against the circumference of the stator case,reither by some suitable means such as springs, resilient material, or simply by the oentrifugalforce generated by rotation. On

this stator case, and slightly farther apart than the; spacing between the vanes, are two tubu-.

latures l. The entire device is filled with a liquid metal. For this purpose we prefer to use a sodium-potassium alloy, since this combines a suitable liquid consistency and good conductivity with the lightness desirable for operation of high speed without generating excessive centrifugal pressures. However, instead of the sodium-potassium alloy, we may use mercury, gallium; or we could use a eutectic bismuth tin lead alloy, or pure alkali metals, although in that case it would be necessary to operate the device at a temperature above the congealing point of these substances, which will generally not be desirable.

The rotor is revolved at a fixed speed, dependent upon the frequency desired, by any constant speed driving device known to prior art.

When the rotor revolves, the vanes pass over the space between the two tubulatures I, and

7 break the electrical circuit between the terminals ,5 which enter the liquid metal in the tubulatures.

in passing over it can decrease the current gradually so that it will give a sinusoidal wave form shown in Figure 2, or any other wave form desired. Figure 2 is a developed view of the inside of the stator I at the point where the tubulatures 1 open into it, and shows one ,of the possible forms of these apertures, designed to give a sinusoidal curve.

The sinusoidal form gives a favorable sine alternating current wave when passed through the transformer.

For operation on triple phase current, the case may have three sets of openings in it, or even more openings and vanes to give polyphase current of any variety or characteristics desired. Figure 2 shows a section through the tubulatures, and shows one of the possible forms which these may be given in order to provide a favorable curve current.

In another modification of the invention, the vanes protrude from apertures in the stator case, and are held by spring pressure or resilient backing against the rotor. In this case the tubulatures I in the stator case only represent entry points for the electrodes 5 and their form is irrelevant so long as their cross section is adequate for carrying the current contemplated. The roor the current, to vary according to a predetermined pattern, as shown, for example, in Figure 4, which represents the developed view of the rotor. When the stator vanes 3 which separate the electrodes pass over one of the points H where the indentations are closed, the current will be interrupted. When a stator vane passes over the point "5'2 where the indentation is widest, the flow of the current will be at a maximum, and between these points a moderate amount of current will flow so that the resultant curvewill be sinusoidal or may haveany otherdesired wave form. Figure 5 more clearly shows the axle 6.

Obviously, many types of 'mechanicalmodifica:

tion of the invention are possible without departing substantially from itsspirit and scope. i-Important features of the invention are the use of liquid metal in the current interrupter'in-such fashion that the interruption occurs between electrodes of liquid metal in thelabs'ence of any gas space where arcing or oxidation or evapora- 'tion could take place, and alsothe employment in such an interrupter of-the very lowspecific gravity potassium-sodiurn alloy, which makes possible a very much lighter construction or faster operation than would have been possible by the use of much heavier metals, such as mercury. The precise proportions 'of sodium and potassium are secondary, so long as the alloy is liquid at the operating temperatures in view: for

- example, an alloy of equal amounts "of sodium permissible to use any other construction material, including metals, provided theseare covered with an insulating surface coating.

As for lubrication, we may-depend on the liquid metal,- filling the interspace 4 I between rotor and stator, or on the inherent characteristics of the vanes, particularly if these are made of plastic material, or, particularly if the-con- 'tacts are made on the rotor side of the liquid metal, on a separate lubricantmedium,- effective in a thin film, such as a sodium fatty acid salt. If the contacts are made on the stator side, we may employ graphite as thelubricant, as graphite is heavier than the alkalimetalalloy and is thus fed to the periphery by centrifugaliorce. The tubulatures I in the stator I are then made sufiiiciently shallow to prevent a settling of the graphite, but will keep the graphite suspended-by the turbulence created in these recesses by the rotary motion of the main body-of the liquid metal.

We may even pack these recesses l with-graphite so that the contact is made between a graphite electrode and the revolving body'of liquid alkali metal alloy. While we prefer to employ recessedelectrodes filled with liquid metal, or with a conducting lubricant such as graphite, we may also employ solid metal electrode inlays of any metalinsoluble in the alkali metal alloy, said inlays being fiush with the wall of the statonand-having a form selected to give a sinoid, or any other desired form and sequence of interruptions, asthe revolving liquid metalandinsulating vanespass thereover in sequence.

' ior any skilled chemist. TEuthectic or low melting alloys withother alkalrmetals such'as cesium,

lithium and rubidium may also be employed, and

"the addition of some percentage of nonalkali metal iswithin the scope of this invention, so

long as said alloy is essentially an alkali metal alloyandisliquid at the operating temperatures contemplated. e may employ pure sodium or potassiumj'depending on friction to generate the necessary-heat to melt the metal, but this is not preferred, as a considerably heavier construction would then be required to withstand the strains in starting.

-While 5 reference has -been :made to members -in the-device as rotorand :fstator, it-is fully realiz'edthat?thesesterms are re1ative,.:that the inner I core 'mayu-be fixed.- and the outerncore brought to-revolve,.and thatithey may evenboth be brought'to revolve,countercurrently,.:for ex- --ample,--by a planetary drive, so that.both;mem- --'-bers l and 2 become. rotors.

-' The invention=is thus of broad'scope, and is not 'to be restricted, except by i the claims, in which it is intended to'cover all novelty inherent in the invention as broadly as possible in view ;ofzprior art.

Having thus disclosed our invention, .WeLcIaim: A currentinte'rruptingdevice comprising a rotor, astator,-said-'rotor and stator-being of electrically insulating material and separated b an-interspace filled with liquid-metal, means for connecting-saidliquid metal with at least "two outside electrodes;- vanes slidably attached to the statorso as ,toform a tightfi-t against. the rotor interruptingthe electrical continuity of the said :"liquid metal and non-continuous indentations in the 'saidrotor.

2.,.A current interruptingdevice comprising a rotor, at Staten-aninterspace'between these filled with liquid metaLLmeans for-connecting said liquidmetal with outsideelectrodes,'saidrotor 'and stator. being of electrically insulating-material; .vanes slidably attached to ".the'stator so as to i .form a tight 'fitjagainst the rotor interrupting-the electrical .continuityof said liquid metal and non- ...continuous sinusoidal. indentations of the said rotor.

3. A; current interrupting device, comprising, in

-ment with: said stator, so as to. completely interrupt the continuity ofsaiddiquid metal except- -=-ing whenupassin overrecesses in the-stator case,

and electrodes, spaced apart, contacting the. said ':-*recesses,:the.i said. liquidumetal. being-an alkali :metal alloy.

:1 4. As .claim.2, the:said..liquidsmetalvbeing an alkali .metal alloy.

5 1 5 A current interrupting-device comprising, in eombinationptwo electrically insulatingemembers =-revolvin-gconcentrically in relationlto eachiother; a' 'closedinterspace:betweenzsaid members; a liquid metal filling saidinterspace ;:at least two insulating "vanes -separating said 'liquidmetal .in at leasttwo portions; atleast twosel'ectrodesicon- 6 tacting said body of liquid metal so spaced that the said insulating vanes periodically interrupt REFERENCES CITED the electrical connection between said electrodes. The following references are of record in the 6. As claim 5, said liquid metal comprising an file of this patent: alkali metal. 5

UNITED STATES PATENTS STUART O. FIEDLER. Number Name Date JOHAN BJORKSTEN. ,461,101 Steams July 10, 1923 

